The present invention relates to a heat transfer printing sheet for use with a heat transfer printer having a heating means such as a thermal head or a laser. More specifically, the present invention relates to a heat transfer printing sheet which can easily produce images having metallic luster when it is used with a heat transfer printer.
Heretofore, the melt transfer printing method has been known. In this method, a heat transfer printing sheet which comprises a substrate sheet such as a plastic film, and a hot- melt ink layer provided thereon, containing a coloring material such as a pigment which is dispersed in a binder such as a hot- melt wax or resin is used; energy is applied image-wise to a heating device such as a thermal head to heat the heat transfer printing sheet, thereby transferring, along with the binder, the coloring material to an image-receiving sheet such as paper or a plastic sheet to produce an image thereon. The image produced by the melt transfer printing method has high density and is excellent in sharpness. The printing method of this type is thus suitable to record binary images such as letters and line images. Further, it is also possible to obtain a multi- or full-colored image on an image-receiving sheet by recording yellow, magenta, cyan and black images one over another by the use of heat transfer printing sheets of these colors.
A demand for easy and simple production of images having metallic luster by utilizing the melt transfer printing method has also been increased. Japanese Laid-Open Patent Publication No. 30288/1988 and the like present a heat transfer recording medium obtained by successively providing, on one surface of a substrate, a releasing layer, a deposited anchor layer, a metal-deposited layer and an adhesive layer. Aside from this, Japanese Laid-Open Patent Publication No. 290789/1988 and the like present a heat-sensitive transfer printing material obtained by providing, on a substrate, an ink layer containing a metal powder pigment and a colorant which are dispersed in a hot-melt vehicle.
In the case where a metal-deposited layer is provided, an image having high brightness, being excellent in visibility can be obtained. In this case, however, a specific apparatus such as a sputtering apparatus is needed to form the deposited layer. Moreover, the deposited layer has no adhesive property in itself, so that it is necessary to provide an adhesive layer as in the prior art. Therefore, there has been a problem in that the production process becomes complicated as a whole.
Furthermore, in the case where an ink layer in which a metallic pigment and a colorant are dispersed is provided, the colorant such as a pigment or a dye and the metallic pigment tend to separate from each other when a coating liquid for forming the ink layer is prepared, so that it is difficult to stably coat the coating liquid onto a substrate. For this reason, the metallic pigment cannot be coated uniformly, and the resulting printing sheet cannot produce an image having high brightness.